The Jaffe reaction (creatinine and alkaline picrate) was studied to elucidate its spectral mechanism and to determine which functional groups are necessary or sufficient for the reaction to occur. 1. Interferences: Only by knowing the molecular mechanism can predictions be made from structure as to probability of interference. We establish that the reaction does not occur through the formation of a carbanion adjacent to the ketone. 2. Suitable evidence was obtained to infer that the carbonyl or a nitrogen group is necessary for reactivity and to suggest that the Jaffe reaction involves a charge transfer complex.